Topics to Be Covered
• The purpose of drilling & blasting in producing crushed stone
• Relative cost of drilling & blasting vs other quarrying activities
• Cost/production opportunities offered with optimized fragmentation
• Factors affecting fragmentation
• Self-evaluation of fragmentation
Why Drill and Blast ?
• Drill and Blast is the first step in the breakage and separation
process. Therefore, it impacts all the subsequent downstream
process efficiencies.
• Drill and Blast is still the most cost effective method to break and
move the large volumes of rock – when done correctly!
Blasting Intensity
Rock Breakage Phases
10000
0%
20%
40%
60%
80%
100%
0.1 1 10 100 1000 Size mm
Cu
m %
pas
sin
g
In-situ
ROM
Crusher
Product
Energy $
Relative Energy and Costs
Specific energy kwh/t
Energy factor
Cost factor
Drill and Blast 0.1 – 0.25 1 1
Load and haul 0.2 – 0.5 1 - 5 2 - 10
Crushing 1 – 2 4 - 20 2 - 10
Generally the harder the rock, the higher the factor.
Lighten Up
Drilling & Blasting Cost - Leverage
10%
11%
1%
15%
30%
33%Drilling
Blasting
Secondary Breakage
Loading
Hauling
Crushing
Drilling & Blasting Cost - Leverage
• Drilling and blasting is the first step in the comminution processes
• A 10% increase in drilling and blasting cost can be compensated by
4.6% reduction in excavation and hauling costs
or 6.4% reduction in crushing
1% decrease in excavation/hauling = 2.1% increase in D&B
or
1% decrease in crushing/benefaction = 1.6% increase in D&B
Traditional Blast Optimization
Blasting effort $/t
$/t
D&B cost
Digging cost
Hauling cost
Optimum
Total mining cost
Crushing cost
Fragmentation Management
$/t
Blasting effort $/t
Optimum
Fines (-$)
Rip-rap (+$)
Best Saleable Product(s) (+$)
? %
? %
? %
Profit = Revenue - Cost
Fragmentation Management
Profit = Revenue - Cost
$/t
Blasting effort $/t
Optimum Profit = _
Revenue Cost
Common Fragmentation Issues
• Oversize breakage costs
• Excavator costs (diggability)
• Crusher costs (throughput)
• Recovery (fines)
Fragmentation Optimization Opportunities
• Better digging and bucket fill factors
• Potential to produce better priced end product
• Reduction in material losses (more saleable product)
• Reduction in blast induced damage
• Consistent crusher throughput and power draw
Factors Affecting Fragmentation
Joint Spacing
Joint Condition
Joint Strike & Dip
Bedding Planes Strike & Dip
Bedding Plane Condition
Bedding Plane Spacing
Rock Strength
Rock Elasticity
Hard/Soft Seams
Grain Size
Sonic Velocity
Geology
Burden
Spacing
Hole Diameter
Stemming
Subdrilling
Delay Timing &
Accuracy
Bench Ht
Staggered/Square
Pattern
Design
Energy
Energy Partitioning
Density
Velocity of Detonation
Coupling
Explosives
Fragmentation
Balancing for Fragmentation
Geology
Geology Optimized Fragmentation
Geology Blast Design
Explosive
Optimal Fragmentation
Structure describes the features which primarily determine the
fragmentation performance of the rock mass.
• Jointing/Bedding
• Defines maximum fragment size
• Influences transmission of stress wave
• Influences gas penetration
• Rock Strength & Elasticity
• Determines how the rock mass responds to the explosive energy
applied
• Influences confinement on explosive
Geology Factors
Blocky
Block size 0.6 – 3 ft
(0.2 – 1 m)
Block size 0.3 – 0.8 ft
(0.1 – 0.25 m) Fractured
Rock Structure
Rock Properties
Density
1.5
1.7
1.9
2.1
2.3
2.5
2.7
2.9
3.1
3.3
Basalt
Dolom
ite
Gneiss
Granite
Limesto
ne
Marb
le
Sandstone
Sandstone
Schist
Slate
Taconite
Compressive Strength
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000
Basalt
Dolom
ite
Gneiss
Granite
Limesto
ne
Marb
le
Sandstone
Sandstone
Schist
Slate
Taconite
Tensile Strength
0
500
1,000
1,500
2,000
2,500
3,000
Basalt
Dolom
ite
Gneiss
Granite
Limesto
ne
Marb
le
Sandstone
Sandstone
Schist
Slate
Taconite
Young's Modulus
0
2,000,000
4,000,000
6,000,000
8,000,000
10,000,000
12,000,000
14,000,000
16,000,000
18,000,000
Basalt
Dolom
ite
Gneiss
Granite
Limesto
ne
Marb
le
Sandstone
Sandstone
Schist
Slate
Taconite
Effect of Rock Stiffness
Pressure
Volume
2
A
B
C
O
High rock stiffness
3 4 5
1
a)
D E Volume
1
2
A
B
C
O
Low rock stiffness
3 4 5
b)
D E
Blast Design Factors
• Hole Diameter
• Influences energy distribution and burden stiffness
• Burden/Spacing
• Influences energy distribution and burden stiffness
• Relationship with joint spacing affects oversize
• Bench Height
• Influences burden stiffness
• Delay Time & Accuracy
• Influences interaction between detonating holes
• Staggered/Square pattern
• Determines distribution of energy in rock mass
Hole Diameter & Burden/Spacing
Free Face Small dia holes
Free Face
Poor fragmentation zones
Large dia holes
Blast Design Factors
• Hole Diameter
• Influences energy distribution and burden stiffness
• Burden/Spacing
• Influences energy distribution and burden stiffness
• Relationship with joint spacing affects oversize
• Bench Height
• Influences burden stiffness
• Delay Time & Accuracy
• Influences interaction between detonating holes
• Staggered/Square pattern
• Determines distribution of energy in rock mass
Blast Design Factors
• Hole Diameter
• Influences energy distribution and burden stiffness
• Burden/Spacing
• Influences energy distribution and burden stiffness
• Relationship with joint spacing affects oversize
• Bench Height
• Influences burden stiffness
• Delay Time & Accuracy
• Influences interaction between detonating holes
• Staggered/Square pattern
• Determines distribution of energy in rock mass
Interhole Delay Time & Fragmentation
(after Cunningham, 2005)
0
0.5
1
1.5
2
2.5
0 1 2 3
ms/ft Burden
X5
0 (
in)
Blast Design Factors
• Hole Diameter
• Influences energy distribution and burden stiffness
• Burden/Spacing
• Influences energy distribution and burden stiffness
• Relationship with joint spacing affects oversize
• Bench Height
• Influences burden stiffness
• Delay Time & Accuracy
• Influences interaction between detonating holes
• Staggered/Square pattern
• Determines distribution of energy in rock mass
Explosives Factors
• Velocity of Detonation
• Indication of energy available
• Indicator of energy partitioning (shock vs gas)
• Determines how explosive energy is applied to rock mass
• Density
• Influences total explosive energy available in a hole
• Coupling
• Influences transfer of explosive energy to rock mass
Explosive Selection
c)
Pressure
Volume
2
A
B
C
O
Rock stiffness
3
4 5
1
a)
D E Volume
1
2
A
B
C
O
Rock stiffness
3 4 5
b)
D E
2
C
O
3 4 5
1
Volume
2
A
C
O
3 4 5
1
Volume
Pressure B
Rock stiffness
D E
C
O
1
Volume
2 3
4 5
A
B
d)
D E
Rock stiffness
Hard and Brittle Rock Soft and Plastic Rock
High
VOD
Low
VOD
Explosive Selection to Meet Rock Structure and Strength Properties
Structures
Str
en
gth
High VOD
High density
Medium VOD
High density
Low VOD
Low density
High VOD
Low density
Explosive Selection to Meet Blast Objectives
Th
row
req
uir
em
en
t
Low VOD
Med-High density High VOD
High density
High VOD
Med density
Low VOD
Low density
Fragmentation requirement
In Summary Fragmentation Results. . .
Have a significant impact on quarry economics
Therefore, Fragmentation Optimization …
• Should consider all the downstream processes rather than just drill and blast costs
• Should consider quality as well as quantity
• Should be site specific
• Should be flexible to cope with site specific changes and market conditions
‘Take Home’ Questions on Fragmentation
• Does the shovel/loader bucket fill with a single smooth pass?
• Does the shovel/loader remain stable during digging (no rocking or violent
movements)?
• Does the muckpile flow during digging?
• Do the haul trucks dump at the crusher without delay?
• Is the throughput and power draw of the crusher consistent?
• Is secondary breakage required on a regular basis?
• Are the desired product sizes produced without waste (fines or other
unsaleable/low profit products)?